The need for very large projection systems like on a building wall or in a large inflatable dome, able to cover a crowd of people and where the projection must be able to project 360 degrees horizontally and 180 degrees vertically, is a big challenge for current projection technology. It is common for such installations to combine overlapping displays from different projectors. In U.S. Pat. Nos. 6,377,306; 6,525,772 Johnson et al. determined that, on a non-lambertian surface, the overlap must be 25% or more. To achieve a quality of rendering, alignment and matching of the projectors, it is mandatory to realize multiple calibration aspects of the system, and it is a time-consuming task, even for experienced personnel.
For a group of projectors to achieve a single seamless, uniform, and larger image, precisely positioned on projection surfaces, there are numerous issues to overcome. The type of corrections generally contemplated herein includes blending imagery correction across projectors so that the total intensity of a region overlapped by multiple projectors is of similar intensity to the rest of the projection surface (Harville, 2006). Further, a geometric calibration (wrap) of the imagery projected to a screen or a complex static surface like building floors, walls and ceilings, or in a temporary one, such as an inflatable dome, must to be done. For manual geometric calibration, the state of the art generally involves the application of substantial precision, which is tedious to achieve. In U.S. Pat. No. 8,777,418, Wright et al. presented an automatic calibration method, but this method requires multiple iterations to operate and requires markers on the screen. In U.S. Pat. No. 9,369,683, Timoner et al. presented both manual and semi-automatic calibration methods using markers.
Projection-based displays suffer from geometric distortions, sometimes on a per-color channel often as a result of imperfect optics of projectors. They also suffer from intensity variations within and across projectors, color sheens, color mismatches across projectors, varying black levels, different input-output curves, etc. The usage of different kinds of projectors or combining old projectors with brand new ones in a multiple projector configuration can produce significant intensity and color disparity on the projection surface. In U.S. Pat. No. 7,038,727, Majumder et al. presented a method to correct intensity variations across projectors.
Color and intensity changes both across projectors and also specifically for each unit must be corrected in order to achieve compensation for the use of multiple units of projection (Pagani, 2007). In U.S. Pat. No. 6,456,339, Surati et al. disclosed the use of cameras and image processing via a pixel correction function and a lookup table to simplify the aligning and matching processes of projectors by providing, after processing, modified images with altered geometry, color and brightness. The use of one or an array of optical sensors, such as calibrated color cameras, to obtain feedback from each projector's projected pixels allows for registering, calibrating and correcting each of the projected pixels to achieve a single seamless, uniform and calibrated image on the projection surface. Methods for calibrating (registration, blending, intensity, color) multiple projector systems to produce a seamless single image with high quality reproduction of color, uniformity and intensity exist, but some manual or semi-manual operation must be done to complete the process. This is particularly problematic for installations that have to be moved and re-installed rapidly, such as with an itinerant projection in a dome where multiple projection shows are provided one after the other. If an element of the projection system (projector, camera, lens, etc.) is changed, moved or just slightly unaligned, a recalibration must be done rapidly between two shows.
During the calibration process, environmental conditions or interferences can produce detected points that are wrong or mislabeled, making calibration impossible without human intervention to manually correct the problem or to reinitiate the calibration process. In U.S. Pat. No. 7,893,393, Webb et al. presented a method for such detected wrong or mislabeled points, but this method requires the parametric surface's equation to operate.
In order to address the above drawbacks, a desired method should provide a quick automatic calibration function including morphing, blending, color, brightness and precise positioning of the corrected composite image on the projection surface to be performed after casual or routine projector and camera placement or changes.
The following US patents disclose other systems that are related to the present invention: U.S. Pat. No. 6,618,076, Sukthankar et al.; U.S. Pat. No. 7,306,341, Chang; and U.S. Pat. No. 9,195,121, Sajadi et al.